1.已知a+b=3,a+²b²=8,求a²+3ab+b²2.已知x+y+z=5,xy+yz+zx=9,求x²+y²+z²的值²(...的平方,
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![1.已知a+b=3,a+²b²=8,求a²+3ab+b²2.已知x+y+z=5,xy+yz+zx=9,求x²+y²+z²的值²(...的平方,](/uploads/image/z/5933647-55-7.jpg?t=1.%E5%B7%B2%E7%9F%A5a%2Bb%3D3%2Ca%2B%26%23178%3Bb%26%23178%3B%3D8%2C%E6%B1%82a%26%23178%3B%2B3ab%2Bb%26%23178%3B2.%E5%B7%B2%E7%9F%A5x%2By%2Bz%3D5%2Cxy%2Byz%2Bzx%3D9%2C%E6%B1%82x%26%23178%3B%2By%26%23178%3B%2Bz%26%23178%3B%E7%9A%84%E5%80%BC%26%23178%3B%28...%E7%9A%84%E5%B9%B3%E6%96%B9%2C)
1.已知a+b=3,a+²b²=8,求a²+3ab+b²2.已知x+y+z=5,xy+yz+zx=9,求x²+y²+z²的值²(...的平方,
1.已知a+b=3,a+²b²=8,求a²+3ab+b²
2.已知x+y+z=5,xy+yz+zx=9,求x²+y²+z²的值
²(...的平方,
1.已知a+b=3,a+²b²=8,求a²+3ab+b²2.已知x+y+z=5,xy+yz+zx=9,求x²+y²+z²的值²(...的平方,
1.已知a+b=3,a²+b²=8
那么ab=[(a+b)²-(a²+b²)]/2=(3²-8)/2=1/2
所以a²+3ab+b²=8+3*1/2=19/2
2.已知x+y+z=5,xy+yz+zx=9
那么(x+y+z)²=x²+y²+z²+2(xy+yz+zx)=x²+y²+z²+18=25
所以x²+y²+z²=7
﹙x+y+z﹚²=5²=25,展开得到2xy+2yz+2zx+x²+y²+z²=25,所以x²+y²+z²=16 微笑